The present invention generally relates to a pulse generator for measuring the magnitude of angular displacement (angle of rotation) of a shaft.
The angle of rotation of a shaft is measured in many different devices, particularly in devices for measuring the number of revolutions of a shaft in an odometer or speedometer, in counters for liquids, etc. In gasoline stations, for example, the gasoline drawn from the reservoir actuates a pump to drive a shaft whose rotational angle is proportional to the quantity of gasoline dispensed. The shaft may perform two revolutions, for example, for each liter of gasoline dispensed. In the conventional gasoline station pumps the shaft drives a counter which indicates the quantity of gasoline dispensed and/or the price to be charged for this quantity.
The manufacture of such a mechanical counter is expensive. Moreover, a counter of this type requires substantial space and frequent adjustments for maintaining the prescribed accuracy. Also, recalibrations necessitated by changes in price are quite complicated. When small quantities of fluid are dispensed, for example at a low pump speed, the measuring accuracy is often unsatisfactory because the torque acting on the shaft is so small that it is unable to overcome the friction in the counter.
German Pat. No. 831,022 discloses a counter for a gasoline pump in which the shaft drives a disc whose edges are provided at regular intervals with permanent magnets which generate electrical pulses in a coil by induction as the shaft rotates. In order to assure that such an electrical signal transmission between the shaft and an electronic counter is accurate within 1-2 ml, either the disc diameter should be large enough to accommodate about 500 permanent magnets in even distribution over the circumference of the disc, or an appropriate transmission ratio must be provided between shaft and disc. An adherence to the first condition has the result that the pulse generator requires substantial space, while the latter solution requires a complicated and expensive transmission mechanism. It is another drawback of the pulse generator disclosed in the above-mentioned German patent that its effect is based on the measurement of a change in flux. With low pumping speeds the change in flux may become so small that the generated signal is too weak to be sensed, which leads to similar erroneous measurements as with the purely mechanical counters.